The present invention relates to the art of induction heating and, more particularly, to an inductor for heating the working and root surfaces between adjacent gear teeth.
The present invention is directed to an improved inductor for use in connection with the hardening of the circumferentially opposed working surfaces of adjacent gear teeth and the radially outwardly facing root surface between the teeth. It is of course well known in the induction hardening field to harden the working surfaces of adjacent gear teeth by inductively heating the surfaces and immediately thereafter quenching the surfaces. It is further well known to achieve such induction heating by means of a U-shaped inductor comprised of an electrical conductor having parallel legs extending radially of the gear teeth in axial spaced relationship and a nose or bridging portion therebetween which is received between the adjacent teeth. Such a nose or bridging portion has a profile corresponding generally with that of the working and root surface between the adjacent teeth. The inductor is energized by a suitable power source, and the gear and inductor are generally relatively displaced axially to progressively move the inductor axially between the adjacent teeth. When the inductor passes through the space between the teeth, the circumferentially opposed working surfaces and the root surface therebteween are progressively heated, and by providing a quenching arrangement adjacent the trailing end of the inductor, the heated working and root surfaces are immediately quench hardened.
Such inductors heretofore provided for heating the working and root surfaces between adjacent teeth of a gear during a quench hardening operation have not provided satisfactory results with respect to achieving a desired uniformity of the depth of the heat pattern along the circumferentially opposed working surfaces and through the root area between the teeth. In this respect, previous inductor constructions have resulted in overheating the radially outer ends of the teeth as a result of the time required for the nose portion to achieve a desired depth of heating pattern in the root portion between adjacent teeth. Overheating of the radially outer ends of the working surfaces between adjacent gear teeth is undesirable in that the heating patterns on circumferentially opposite sides of the same gear tooth at the radially outer end thereof overlap one another. Since such overlap occurs on one side of a given tooth following the quench hardening of the working surface on the other side of the given tooth, the subsequent heating of the one side causes tempering or annealing of the previously hardened working surface adjacent the outermost portion of the gear tooth which decreases its hardness. While such overlap can be avoided by increasing the scanning speed, the latter results in an undesirable depth of the heating pattern in the root area between adjacent gear teeth. Since a uniform depth of the heating pattern and thus the hardened surface is desired throughout the working and root surfaces between adjacent teeth, the latter procedure does not solve the problem.
One previous effort to solve the foregoing problem is disclosed in U.S. Pat. No. 3,185,808 to Sorensen et al wherein one leg of a U-shaped inductor is provided with a copper block radially outwardly of the nose portion of the inductor. The copper block controls current flow through the inductor so as to limit the heating effect of the inductor near the radially outermost portions of the gear teeth as the inductor is moved axially between the teeth. While the latter structural arrangement does alleviate the problem to some extent, proper adjustment of the low resistance copper block relative to the nose is necessary to achieve the desired control of the heating effect, and such adjustment is a time consuming operation and requires testing to be sure that a given adjustment provides the desired control with respect to gear teeth to be hardened. Moreover, such a structural arrangement controls the heating effect so that the radially outer portions of the working surfaces of adjacent teeth are not overheated in response to a scanning speed which enables the desired heating in the root area between adjacent teeth. Accordingly, the scanning speed is the lower speed required to achieve the desired heating of the root area with control of current flow to prevent overheating of the radially outer surface areas of the teeth at the lower speed. Thus, the scanning speed is not optimized and this results in increasing the time required to inductively heat and harden all of the teeth on the outer periphery of a given gear. This, of course, results in a reduction in production rate.